Homework 6 Organic Chemistry MCAT Review Summer 2012 Brent Iverson

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1 omework 6 rganic hemistry MAT Review Summer 2012 Brent Iverson 1

2 1. Fill in each blank with the word that best completes the following sentences about NMR. The two most important isotopes for organic chemistry structure determination by NMR are 1 and. 13 f these two, 1 is a common isotope and the predominant isotope found in molecules, while is relatively rare. 13 Nuclei with spin quantum number 1/2 are quantized in one of two orientations: +1/2 (lower energy) or -1/2 (higher energy) in the presence of an external magnetic field, that is, with and against the external field, respectively. The difference in energy between nuclear spin states is proportional to the strength of the magnetic field experienced by the nucleus. Electron density is induced to move in a strong external magnetic field, and this movement induces a magnetic field that is opposed to the external magnetic field. This has the effect of shielding the underlying nuclei from the external magnetic field. All other factors being the same, the signal for an 1 atom with greater electron density around it will come at lower ppm in an NMR spectrum compared to a similar 1 atom with less electron density. The spins of adjacent nuclei influence each other. If 1 atoms are no more than three bonds apart, the spin states couple. 2

3 1. (cont.) In the FT NMR method, the FT stands for Fourier. transform The basic idea is that a short pulse using a range of radio frequencies is used to flip the spins of all of the hydrogen nuclei at once. Then, the nuclear spins relax back to the +1/2 spin state and when they do, they emit electromagnetic radiation at the precise frequency at which they absorb. 2. Suppose a relative of yours is having an MRI. In no more than four sentences, explain to them what is happening when they have the MRI scan. There are a minumum of 7 key points here. The popular medical diagnostic technique of magnetic resonance imaging (MRI) is based on the same principles as NMR, namely the flipping (i.e. resonance) of nuclear spins of protons by radio frequency irradiation when a patient is placed in a strong magnetic field. Magnetic field gradients are used to gain imaging information, and rotation of the gradient around the center of the object gives imaging in an entire plane (i.e. slice inside patient). In an MRI image, you are looking at individual slices that when stacked make up the three-dimensional image of relative amounts of protons, especially the protons from water and fat, in the different tissues. 3

4 3. ircle the molecule that corresponds to the NMR spectrum shown below. N 4

5 3. ircle the molecule that corresponds to the NMR spectrum shown below. F 5

6 3. ircle the molecule that corresponds to the NMR spectrum shown below. 6

7 3. ircle the molecule that corresponds to the NMR spectrum shown below. Br

8 8 4. In the boxes provided, place that letter (A, B,, etc.) that corresponds to the signals in the spectrum provided below. E B A E E B A B E

9 5. For the following structures, draw a circle around the terms that provide the most accurate description. 2 2 Aldohexose Ketohexose Aldopentose Ketopentose Pointy toes This structure is a: Furanose Pyranose Monomeric carbon Anomeric carbon Polymeric carbon Aldehyde carbon omatose Bloody nose 2 α-1,6-glycosidic bond β-1,6-glycosidic bond α-1,5-glycosidic bond β-1,5-glycosidic bond α-1,4-glycosidic bond This molecule is a: Aldohexose Ketohexose Aldopentose Ketopentose Pointy toes This structure is a: Furanose Pyranose omatose Bloody nose 2 β-1,4-glycosidic bond α-1,3-glycosidic bond β-1,3-glycosidic bond α-1,2-glycosidic bond 2 α--glucose β--glucose βββ--glucose ΔΓ--Glucose β-1,2-glycosidic bond 9

10 6. For the following carbohydrates, draw a circle around all of the -carbohydrate(s), and draw a rectangle around all of the L-carbohydrate(s). n the two first two lines below the four structures, indicate whether each is an aldose or ketose, and whether each is a pentose or hexose, respectively. n the third line below each structure, construct a compound name from all of these elements. For example, answers might be L-ketopentose or L-aldohexose. Finally, on the fourth line under each structure write the specific name (i.e. -glucose) for each structure. You should use table 25.1 or other structures named in the book (5th Ed. Brown, Foote, Iverson and Anslyn) to identify these exact sugar names. (You will NT need to know them for the MAT). 2 L aldose aldose ketose aldose (aldose or ketose?) hexose hexose hexose pentose (pentose or hexose?) -aldohexose -glucose L-aldohexose L-glucose -ketohexose -fructose (pg 1009) -aldopentose -ribose (compound name) (exact name) 2 2 For the disaccharide of glucose on the left, draw a circle around any glucose residue that is/are a. raw a box around any glucose residue that is/are b. Next, draw a box around the glyocosidic bond linkage. Finally, circle all anomeric carbon atoms. 10

11 7. raw the two most important resonance contributing structures of the amide shown below. Be sure to show all lone pairs and formal charges. You do not have to draw arrows on this one. N N N 8. n the lines, indicate the hybridization state of each atom indicated by the arrows. sp 2 N 2 sp 2 2 sp 3 3 N 3 N sp 2 sp 3 9. n the following structure circle all of the -N bonds that NT RTATE. N 2 nly protonated at low p, as in p N N 3 For the above stucture, is this the appropriate protonation state for p 2.0, 7.0, or 10.0? 2.0 Notice This 11

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Homework Problem Set 11 Iverson CH320N Due Friday, May 5

Homework Problem Set 11 Iverson CH320N Due Friday, May 5 omework Problem Set 11 Iverson 320 Due Friday, May 5 AME (Print): SIGATURE: hemistry 320 Dr. Brent Iverson Problem Set 11 April 28, 2017 Please print the first three letters of your last name in the three